Pc problem help!

My pc starts but doesn't have output to monitor, keyboard and mouse... However there is output to my external hdd. I just added 2gb ram a few months ago. A geforce 8600 graphics card since december, internal 160gb hdd. Xp home edition. Hp compaq dx7300....

Intel core 2 duo.

My answer is one of the case:
If you are using 2 RAM means there may be a short circuit is possible... Check that

There's some kind of hardware problem. It's not actually starting up at all it's just providing power to the fans and everything. I dunno what failed but the RAM is a good guess. Try jiggling the RAM, taking it in and out, etc. You can also try taking the battery out and putting it back in. If you have your motherboard manual there should be a CMOS reset jumper you can use. Just put the jumper on the reset pins, wait 10 seconds, then put it back where it was. If you have your old RAM you can also try that and see if it works.

Other possible causes are motherboard or CPU, but RAM is most common. Video card wouldn't cause that unless your motherboard doesn't have onboard video. Hard drive would show a startup screen and then show a boot error before starting windows, but at least you'd see something.

Sometime it starts correctly and every thing goes alright, most of the time it doesn't and does like I said above. Help